The present invention relates to a PLC (programmable controller) for distributed control and a distributed control system including a plurality of PLCs for distributed control connected to one another.
Recently, in order to control mechanical equipments positioned at a plurality of places for factory automation, a distributed control system including a plurality of PLCs controlling mechanical equipments connected to one another has been known (for example, see Patent Document 1).
Such a distributed control system according to the related art uses a method in which adjacent PLCs are connected to each other by a plurality of I/O wiring lines and a plurality of signals are transmitted through the I/O wiring lines. Since safety PLCs for securing the safety of control objects are required to correctly transmit a plurality of control signals, such as interlock signals, according to a plurality of control objects to one another, the above-mentioned method is very effective.
Patent Document 1: JP-A-2002-358106
However, in the above-mentioned method, an operator is required to manually check the connection between the PLC terminals connected to the individual I/O wiring lines in order to determine whether communication by each wiring line is correctly performed, resulting in a low maintenance property. Further, since the plurality of I/O wiring lines should be provided between the PLCs, the number of PLCs increases, and thus the cost increases.